Apparatus for heat extraction



Oct. 17, 1944. R, T. FIELDS 6 APPARATUS FOR HEAT EXTRACTION I FiledApril. 29, 1943 Reuben d3 INVENTOR.

ATTORNEY Patented Oct. 17, '1944 I UNITED STATES PATENT OFFICE APPARATUSFOR nna'r nxrlmcrron 1 Reuben T. Fields, Arlington,gN. J., assignor toE. I. du Pont de Nemours & Company,-Wilmlngton, D el., a corporationofDelaware Application April 29, 1943, Serial No. 5,026

- in the chemical and related arts by means of a high boiling liquid atboiling temperature.

It is an object of this invention to provide an improved system. ofheating by means of high boiling liquids. A more specific object is toprovide a method of heating chemical and relatedapparatus, which is freefrom moving mechanical parts. Another object is to provide such a methodwhich may be operated with a high degree of. efllciency, a high heatoutput, and a minimum of sjcisims. (o1. 126-3435) of heating contactwith the walls of such apparatus or inserted directly-into reactingfluids or polymerization media. The heatingfluid return line 8 serves toconnect the outlet side of the heat exchange unit 3-with the boiler 2.An expansion chamber, Suhaving a vapor dome in its upper part isinserted at the high point in the heating fluid rev turn line 8. Thisexpansion chamber 5 is provided with a valve "6 iorbleedin g-offgases orapplying pressure and a pressure gauge 1. This entire closed loopsystem-is lagged with heat 'incontrol. Still another object is toprovide a method of heating chemical apparatus which can be controlledover a narrow range of temperature. Still further objects will becomeapparent from the following description of theinvention.

These objects are accomplished according to the method of this inventionby heating a high boiling liquid in the boiler of a closed systemsulation material Ill.

The heatingsystem 01' this invention operates at the boiling point ofthe liquid employed as the i heat transfer medium. However, since theboiling point of any liquid isdependent upon the absolute pressure onsaid liquid, the operating temperature of the heating system ofthisinven- -tion may be varied by adjusting the operating Thus, byutilizing eitherpressure of the system'- lsubatmospheric pressure,

a partial vacuum, or

. atmospheric pressure or elevated pressure, it is comprising a boiler,a riser, a heat exchange unit,

an expansion chamber situated'on the outlet side possible-with a heattransfer liquid such as diphenyl, diphenylether, or mixtures of thesetwo,

alkylated-diphenyl and diphenyl ether, retene,

of the heat exchange unit and at the topmost portion ofthe heatingsystem, and a return line connecting the heat exchange unit to the lowerportion of the boiler. The system is filled with a heat transfer liquidto such an extent that when said system is heated to the operatingtemperaf ture the liquid level'will be within the expansion chamber. Inoperation 01' the system, bubbles of vapor form in the boiler and ascendthrough the riser tube to the heat exchange means where heat isextracted from the vapor-liquid mixture thereby causing the vapor tocondense, which condensate then flows by way' of the return tube to theboiler because of the unequal densities existing between the hydrostaticheads A of thereturn line and the riser line' of the heating system.

' The invent on-will be further described in greater detail withreference to the accompanying drawing which is provided in illustrationof a practical embodiment of it.

In the drawing, there is a diagrammatic representation of suitableapparatus which may be employed in the operation of the invention, theboiler unit 2 is provided with a heating'unit I,

a heating fluid outlet line or riser 9, and a heating fluid return line8. The heat exchange unit 3 includes heating coils l surrounded by theobiect to be heated. Thus,they may be embedded in the walls of achemical reaction vessel, extrusion press, or thelikefor maintained inintini ate etc., to operate the heating systems of this invention attemperaturesover a wide range, e. g.. between 120 C. to 320 0., or evenhigher, if desired;

- It is particularly useful for llquel'ying plasticto furnishthe heatnecessary to boilthe liquid.

Thus, the heating means 1 of the drawing may constitute an electricresistance 'or induction heating element, or a fuel-fired unit, e. g., agasflred, oil-fired, or coal-fired unit, or the like.

Although the drawing and description herein has represented the processor, this'invention as operating with only'cne heating loop and heatexchange unit, it is entirely practical to operate more than one heatingloop i'romthe same boiler provided theheat output of the heat'supp y Isufllcient to furnish the requisite amount of heat to the separate heatexchange units, and that all heating loops operate at the sametemperature.

a The line leading. from the top of the boiler to the heat exchange unit9, herein referred to as the "riser" should preferably ascend directlyfrom the boiler to the heat'exchange unit. .A perpendicular orsubstantially perpendicular riser is out the heating apparatus. thevapor enterthe heat exchange unit, they most advantageous. However, ariser which ascends at a marked angle can b'e-used provided that asubstantial upward pitch be present in all sections of the line. Thus,the riser preferably should be free of sections possessing adownwardpitch, for these sections generally lead to difficulties whenthe operation of the heating system is begun. Furthermore, the higherthe heat exchange unit 3 is above the boiler 2, the more rapid andeflicient will be the circulation. The expansion chamber 5 provides forthe fluid volume expansions which result during operation of the systemand for the accumulation of vapors or gases and vaporous decompositionproducts. This expansion chamber should be situated at the high point ofthe system. When the liquid level is within the expansion chamber acontinuous liquid circuit is formed throughout the various sections ofthe apparatus.

The heat exchange unit 3, as previously stated, comprises a series ofcoils 4 surrounded by the mass to be heated. The illustrated unit 3 maybe replaced by substantially any variety of heat exchange unit, e. g., aheat-jacketed chemical reaction vessel. The heating method of thisinvention is of special utility in the case where the unit 3 has coilswhich have a small rise or pitch. It is especially useful in a conical,freedraining superpolyamide melting unit.

The method by which heating is accomplished according to the process ofthis invention Will be further illustrated by reference to the follow?ing example:

The system illustrated in the drawing is charged with an amount of amixture of diphenyl and diphenyl oxide, sufficient to reach into theexpansion chamber when the contents of the system are raised to theoperating temperature. Since the expansion chamber is the highest pointin the system, when the liquid level of the system reaches this chamber,the liquid forms a complete loop from the boiler, through the riser, the

heat exchange unit, and the return tube. Heat is applied by means of theheating unit I to the boiler so as to cause the heating liquid, composedof 26.5% diphenyl and 73.5% diphenyloxide, contained therein to boil.The pressure on the system is adjusted to zero pounds gauge. As theliquid boils in the'boiler, bubbles of vapor ll rise in the liquid andascend into the riser tube of the heating system. As soon as this risercontains vapor bubbles as well as liquid, the hydrostatic head A in therisertube 9 is less than that of the hydrostatic head A in the returntube 8. This difference in hydrostatic heads results in a forcedcirculation of the heating fluid through- As the bubbles of arecondensed into liquid which is then returned to the boiler. The forcedcirculation of the heating fluid continues so long as any vapor is beingproduced in the boiler. Operating in this fashion, the heat exchangeunit 3 can be maintained constantly and easily at a temperature of 258C.In another case, the temperature of the unit 3 is maintained at atemperatureof 279 C. by adjusting pressure on the system to 18 poundsper square inch gauge. In still another case, the temperature of theunit 3 is maintained at a temperature of 121 C. by adjusting thepressure to 29.5 inches of'vacuum. Y

Since this system combines the virtues of both vapor heat and liquidcirculation, temperature control may be effected by either thermostaticor manostatic control. In addition, since the invention employs acompletely closed system with no moving parts and valves or packingglands in the circulation lines, heat losses by the system of thisinvention are small in comparison with mechanical circulation systems.Furthermore, the heating system is capable of much greater output andefliciency than convection or mechanical circulation liquid heatingsystems. Since the system is completely closed, no heating fluid canescape. Decomposition products do not interfere with the operation ofthe system, since they collect in the expansion chamber, from which theymay be removed at infrequent intervals. The process and apparatus ofthis invention, therefore, provide a very eflicient, easily operatedmethod for heating which is free of adverse mechanical difficulties andoffers the advantages of operating at high degrees of efilciency andheat output, close regulation of temperature, high rate of heattransmission, and minimum danger of localized overheating.

The heating system of this invention possesses extreme utility inmelting such materials as the synthetic linear polymers, especiallypolyamides which melt at relatively high temperatures and within arelatively narrow temperature range, but which must not be overheatedbecause of the ease with which they decompose when heated slightly abovetheir melting point. Such polymers are disclosed in U. S. P. 2,130,948and their extrusion in U. S. P. 2,295,942. Furthermore, this heatingsystem is very useful for furnishing the heat necessary to operatechemical reaction vessels.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that the invention is not limited to the specific embodimentsthereof except as defined in the appended claims.

I'claim:

1. A heating apparatus comprising a boiler, a heat exchange unitdisposed above said boiler comprising a coiled tube, a riser connectingthe top of said boiler and the bottom of the coiled tube; an expansionchamber having an expansion zone above said unit and connected to thetop of said coiled tube and a return line connecting the top of thecoiled tube and the boiler, said chamber being partly filled with astable, inert, high boiling liquid so that the entire system below thechamber is filled with said liquid at operating temperatures. a

2. A system for liquefying plastic materials comprising a boiler, a heatexchange unit consisting of a melting unit for plastic materialscomprising a charging vessel having a coiled tube in intimate. heatexchange relationship therewith, a riser connecting said boiler and thebottomof said coiled tube, an expansion-chamber havingan expansion zoneabove said unit and a return line connecting 'the upper part of thecoiled tube and the chamber with the boiler, said chamber being partlyfilled with a stable, inert, high boiling liquid so' that the remainderof the entire system is filled with said liquid at operatingtemperatures.

a return line connecting the upper end of said r 2,860,665 v v 5. Aheating apparatus comprising a boiler, a

tube and the bottom part of said boiler, the lower end or said chamberbeing connected to said return line at the highest point of said line,the

heat exchange unit disposed above said boiler, a riser connecting thetop oi said boiler and the bottom of said heat exchange unit, anexpansion chamber connected to the top of said'unit having an expansiondome, and a return line connecting said unit and chamber with saidboiler, said chamber being disposed above said unit and partly filledwith a high boiling liquid so that the re- 10 mainder of the entiresystem is filled with said liquid at operating temperatures.

' REUBEN T. FIELDS.

